Hidrológiai Közlöny 1972 (52. évfolyam)

10. szám - Horváth Imre: A recirkuláció szerepe eleveniszapos szennyvíztisztító rendszerekben

Hidrológiai Közlöny 1972. 10. sz. 436 The Role of Recirculation Rate in the Activated-sludge Waste Treatment Process* by I. H O R V Á T 11" 1. Introduction The aim of this paper is to present a mathematical analysis of the role of recirculation in the activated-sludge method of séwage treatment. By using mass balance equations, the effect of some of the main variables on treatment efficiency can be determined. 2. Balance Equations The treatment process under consideration comprises an aeration tank of the tank reactor type and a secondary settling tank, from which sludge is recirculated into the former. An operational scheme of the treatment is shown in Fig. 1. It is assumed further, that the Michaelis-Mentenian kinetic model is valid: Ti 1 fir (4) 1 + C

e and that the yield constant can be defined by the relation

: (5) It should be noted that the above balance equations must be considered egzactly because otherwise e.g. the faulty consideration of the role of recirculation is given [1]. Aeration tank Influent A7 V

UG i Ce Settling tank Effluent (1+RQ)Q

V, G

l , C

e Recirculation Excess sludge QR = RQ

• flp, G

R=R

G-G

L, C

e Q.f -RF

• a

v, Gn, Ce

t Fig. 1. Scheme of activated-sludge treatment process with main notations For a numerical description of the recirculation effect, mass balance equations are written for the aeration and settling structures. In using the equations, the ideas of Herbert are followed [1] ,these being widely used in the technology of sewage Under ste;ld

v conditions Eqs. (1), (2) and (3) treatment. The balance equation written for the equal zer

o Substituting the value of n thus obtained from Eq. (2) into Eq. (4), tho following 3. Mathematical analysis oi the recirculation effect-assuming steady conditions 3.1 Substrate concentration in the effluent substrate in the aeration tank is: Qv 'Co + SqQr-Ce - (1 + lt

Q)Q,-C

e - r

8 • G

L • VL

= d C

e d t VL (1) BQQV •RGG

L — (\+1ÍQ)QVGI+ ri-GL - V Ld GL -ke-G

l- Vldü •V

L (2) The balance equation for the activated sludge in the settling tank is: (1 +BQ)QVGL—RQQO • RQGL—Q

v(\ — RF) -Ge— -R

fQ

v-RgGL=—^-VÜ (3) expression results: Ce — A 1 (6) The balance equation for the activated sludge in the aeration tank is: where AD+ke 1 + R

Q(l-R

G 1 * Research Institute for Water Resources Development, Budapest, Hungary. ** This paper is based on the following report: Horváth, I.

: ,,The effect of recirculation rate in the activated sludge waste treatment process", Budapest, 1969. (7) By Eq .(6) the substrate concentration C

e is related positively to the recirculation factor A. The factor A, on which the present paper is focussed, has been originally introduced by Herbert during the analysis of continuous cultures [2]. 3.2 Organic suspended solids in the aeration tank From Eqs. (1) and (2) the suspended solids GL are expressed als GL = —

V-\-[Co-Ce). (8) A + D